This work demonstrates post n-work function (WF) deposition Q-time impact on device Vt instability. Longer Q-time induced Vt shifts that are independent of gate length and number of fins, as seen in Figure 1. The root cause investigations were performed using device characterization followed by elemental analysis of the gate stack (Figure 2). It was found that, the content of oxygen (O2) and Al in the gate stack is well correlated to post n-WF deposition Q-time. The device Vt instability can be explained by oxygen incorporation due to n-WF layer oxidation during the Q-time post n-WF deposition and the corresponding reduction of Al diffusion into the high-K capping layer [2, 6]. In this work, n-WF layer thickness/composition was optimized to enable immunity to a larger Q-time limit for volume manufacturing, as demonstrated in Figure 3 from n-WF layer recipe group A to group C. The reliability impact of the gate stack was also assessed. Device benefits such as Tinv scaling and thereby Ion-Ioffperformance improvement was also demonstrated without compromising the reliability.
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